This invention relates to a method for refining glyceride oils by contacting the oils with an adsorbent capable of selectively removing trace contaminants. More specifically, it has been found that novel organic acid-treated amorphous silicas of suitable porosity have superior properties for the adsorption of phospholipids and associated metal containing species from glyceride oils. This facilitates the production of oil products with substantially lowered concentrations of these trace contaminants. The term "glyceride oils" as used herein is intended to encompass all lipid compositions, including vegetable oils and animal fats and tallows. This term is primarily intended to describe the so-called edible oils, i.e., oils derived from fruits or seeds of plants and used chiefly in foodstuffs, but it is understood that oils whose end use is as non-edibles are to be included as well. It should be recognized that the method of this invention also can be used to treat fractionated streams derived from these sources.
Crude glyceride oils, particularly vegetable oils, are refined by a multi-stage process, the first step of which is degumming by treatment typically with water or with a chemical such as phosphoric acid, citric acid or acetic anhydride. Gums may be separated from the oil at this point or carried into subsequent phases of refining. A broad range of chemicals and operating conditions have been used to perform hydration of gums for subsequent separation. For example, Vinyukova et al., "Hydration of Vegetable Oils by Solutions of Polarizing Compounds," Food and Feed Chem., Vol. 17-9, pp. 12-15 (1984), discloses using a hydration agent containing citric acid, sodium chloride and sodium hydroxide in water to increase the removal of phospholipids from sunflower and soybean oils. U.S. Pat. No. 4,049,686 (Ringers et al.) discloses dispersing a substantially concentrated acid or anhydride in the oil, adding water and separating the aqueous phase containing gums and phospholipids. It is disclosed that acetic acid, citric acid, tartaric acid, lactic acid, etc. are most preferred. In addition to the use of organic acids during oil degumming, citric acid and other weak acids have been used as trace metal deactivating agents to promote taste and oxidative stability of edible oils.
After degumming, the oil may be refined by a chemical process including neutralization, bleaching and deodorizing steps. Alternatively, a physical process may be used, including a pretreating and bleaching step and a steam refining and deodorizing step. Physical refining processes do not include a caustic refining step. State-of-the-art processes for both physical and chemical refining are described by Tandy et al. in "Physical Refining of Edible Oil," J. Am. Oil Chem. Soc., Vol. 61, pp. 1253-58 (July 1984). One object of either refining process is to reduce the levels of phospholipids, which can lend off colors, odors and flavors to the finished oil product. In addition, ionic forms of the metals calcium, magnesium, iron and copper are thought to be chemically associated with phospholipids and to negatively effect the quality and stability of the final oil product.
The removal of phospholipids from edible oils has been the object of a number of previously proposed physical process steps in addition to the conventional chemical processes. For example, Gutfinger et al., "Pretreatment of Soybean Oil for Physical Refining: Evaluation of Efficiency of Various Adsorbents in Removing Phospholipids and Pigments," J. Amer. Oil Chem. Soc., Vol. 55, pp. 856-59 (1978), describes a study of several adsorbents, including Tonsil L80 (TM) and Tonsil ACC (TM) (Sud Chemie, A.G.), Fuller's earth, Celite (TM) (Johns-Manville Products Corp.), Kaoline (sic), silicic acid and Florosil (sic) (TM) (Floridin Co.), for removing phospholipids and color bodies from phosphoric acid degummed soybean oil.